It is generally considered poor form to begin a sentence with a numeric digit. For example,
4% of people are old.
Four percent of people are old.
What is the rule when you need to begin a sentence with a chemical name that should not be converted to a word?
2-chloroprocaine is an anesthetic.
It doesn't seem right to capitalize the first letter after the number, because chemicals are not normally capitalized.
2-Chloroprocaine is an anesthetic.
Spelling it out seems inaccurate.
Two-chloroprocaine is an anesthetic.
Rewriting the sentence makes it confusing.
An anesthetic, 2-chloroprocaine, is.